Generated Summary
This article is a reply to a comment on the original study, ‘Unintentional unfairness when applying new greenhouse gas emissions metrics at country level’ (RS19), which critiques the ethical implications of using GWP* (GWP-star), a specific type of greenhouse gas metric, at the country level. The authors of RS19 address the comment, referred to as CCmt, clarifying their original study’s key points and addressing misunderstandings. The reply reiterates RS19’s critique of the potential ethical implications of applying GWP*-like metrics at the country level, highlighting an ethical blind spot in the current GHG metrics literature. The discussion focuses on the ethical considerations of applying GWP*-like metrics, particularly concerning methane emissions and their impact on national accountability and fairness. The authors provide a scientific critique of the ethical implications of using GWP*-like metrics, highlighting the potential for grandfathering historical emissions and its ethical implications. The article then explores the broader debate of ethical implications of GHG metrics and considers solutions to address the identified equity and fairness concerns, providing context on the policy implications of GHG metrics and their impact on international climate policy, particularly in the context of the Paris Agreement.
Key Findings & Statistics
- In the example provided, Abraham, keeping his cows at the level of his father and grandfathers, is assigned 140 and 350 tCO2*-equivalent methane emissions over the first 20 and 50 years, respectively.
- Bethany, who was able to buy ten cows despite her parents not owning any, is assigned 2240 and 2450 tCO2*-equivalent methane emissions during the first 20 and 50 years, respectively.
- Chris, who kept half of the 20 cows of his father, is assigned negative 1960 and negative 1750 tCO2*-equivalent methane emissions during the first 20 and 50 years, respectively.
- Globally (in this case, simply all three farmers together), methane emissions would be estimated at 420 and 1050 tCO2*-equivalent during the first 20 and 50 years, respectively.
- The authors of the article highlight that the application of GWP* to compare methane mitigation contributions between countries without taking into account their historically grandfathered starting position is deeply unfair.
Other Important Findings
- RS19 establishes that applying GWP*-like metrics at any but the global level raises ethical questions of how historic and on-going methane emissions are nationally accounted for in a fair and equitable manner.
- RS19 provides a discussion and potential solutions to address this issue. RS19 does not discuss equity considerations in relation to (historic) CO2 emissions, and neither does it provide a comprehensive assessment of all ethical implications of treating different GHGs with a common metric.
- For CO2, a long-lived GHG, cumulative emissions are linked approximately linearly to global average temperature increase.
- For a short-lived GHG, like methane, annual emissions over time determine largely the resulting warming effect, and changes in their emissions rate cause this warming contribution to increase or decrease.
- A metric like GWP* focuses on capturing these changes in warming when aggregating time series of different GHGs into CO2-equivalent emissions, not on the total warming per se. This focus results in a different relation between CO2-equivalent emissions and warming that raises new questions of equity and fairness.
- These ethical issues arise from moving away from an emissions-centred metric like GWP-100—where every unit of emissions of a certain GHG is treated equally—to metrics like GWP*, which focus on additional warming and where the treatment of a unit of emissions depends on the emitter and their emission history.
- RS19 outlines how application of the GWP* metric, which focusses on warming differentials, can strongly benefit actors with high historic methane emissions in ways an emissions-focused perspective would not. This potential benefit for high historic methane emitters contrasts with considerations of equity and fairness.
- RS19 explores solutions by looking at the implications of different considerations of equity including redistributing (historic) emissions allowances per capita.
- RS19 outlines real-world consequences of the application of GWP* and outlines how developed countries, some of which have per capita methane emissions that are about an order of magnitude higher than most developing countries, would clearly benefit from the grandfathering perspective that is implied by a direct application of GWP* relative to the recent past.
- The authors suggest that the use of GWP* to compare methane mitigation contributions between countries without taking into account their historically grandfathered starting position is deeply unfair.
- The authors agree that the use of a metric that reflects the impact of all gases on global mean surface temperature makes it easier to include methane in discussions of historical responsibility, not the reverse.
Limitations Noted in the Document
- The authors acknowledge that the comment provided by CCmt does not fully address the point made by the original RS19 study.
- Most of the discussion provided in CCmt does not address the point made by the criticized RS19 study, and seems to start from a misunderstanding of RS19 or from context unrelated to it.
- RS19 does not discuss equity considerations in relation to (historic) CO2 emissions, and neither does it provide a comprehensive assessment of all ethical implications of treating different GHGs with a common metric.
- The authors note that the comment provided by CCmt repeats the already well-established discussion of how GWP* provides a closer link between cumulative CO2-equivalent emissions and global mean temperature increase.
- The discussion misses out on the fact that the mitigation action architecture of the Paris Agreement encompasses more than just a temperature goal.
- The authors emphasize that the ethical blind spot that RS19 describes is not acknowledged in CCmt’s example.
Conclusion
The central argument of the article underscores the potential for unintended consequences and unfairness when applying GWP*-like metrics, particularly at the country level, without accounting for historical emissions. This is especially relevant in the context of methane emissions, where different starting points can lead to significantly different assessments of future contributions, potentially rewarding historical high emitters. The authors clarify that their critique is not merely a technical or scientific point, but a commentary on the ethical and policy implications of these choices. The article emphasizes the need to consider equity and fairness when using GWP*-like metrics, especially in the context of international climate agreements like the Paris Agreement. The authors stress that the choice of the metric impacts the policy context and the interpretation of international treaties, underscoring that the decision to apply a given metric has significant implications. They highlight the importance of recognizing the potential for such metrics to be misused, resulting in unfair outcomes or inconsistencies within a policy framework. The authors assert that the limitations of GWP* metrics are not inherent to the metric itself, but arise from the specific way it is applied within a particular policy framework. The article concludes by reinforcing the need for a more nuanced and interdisciplinary approach to understanding and communicating the implications of using GWP* and other similar metrics in climate policy, emphasizing the importance of ethical considerations in the design and implementation of climate mitigation strategies.